Deadly cone snails use "weaponised" insulin to disable whole schools of fish for their dinner, researchers have found.
The sea snails have been found to create a venom cocktail that causes blood glucose levels in fish to plummet suddenly, leaving them powerless to defend themselves as the predator swallows them slowly.
Researchers from the University of Utah found that when a synthetic form of the snail insulin was injected into fish, blood glucose levels fall dramatically. It also disrupted swimming behaviour in fish exposed through water contact.
"This is a unique type of insulin. It is shorter than any insulin that has been described in any animal," said senior author Baldomero M. Olivera. "We found it in the venom in large amounts."
Coral snails are found in most tropical marine waters. Each different species makes a distinct venom compound to target their favoured prey. Conus geographus – the snail in question – has killed many people as a result of accidental encounters.
The study, published in the Proceedings of the National Academy of Sciences, found that Conus geographus traps fish by releasing the insulin venom into the water. They protrude their stretch mouth-like parts and fire the insulin at the fish, after which they engulf the fish.
Lead author Helena Safavi-Hemami said: "It is very unlikely that it is serving a different purpose."
Researchers found two sequences in the snail's venom gland that were very similar to that of the hormone insulin. These genes were also expressed more highly than some of the other venom toxins. Further analysis showed it contained abundant amounts of insulin.
However, researchers also note they found no evidence of fish insulin in the venom – so they re-created the venom to see what would happen when directly tested on fish.
The authors say their findings could provide information on how the human body controls blood sugar and energy metabolism.